SMALL ALKALINE CELLS:
Hermetically sealed Ni-Cad cells are produced in the same size and shape as their primary counterparts. They are small, portable and maintenance free, but have the added advantage of being rechargeable.
The plates are constructed in a similar manner to the larger Ni-Cad cells, the separator being a thin porous material. The electrolyte is fully absorbed by the plates and separator in a similar manner to the Varley type cell. With steel or plastic being used for the case.
Special vents are fitted to each cell, these allow the escape of gas but prevent the entry of oxygen and electrolyte leakage.
The nominal voltage of a fully charged cell is 1-25 volts and these can then be interconnected to form batteries.
A 10 hour rate capacity is generally used with an end of life voltage of 1.1 volts, it is possible to discharge the cells further but damage will occur if allowed to go below 1 volt.
Charging should be carried out using a constant current at the 10 hour rate, total charge taking approximately 14 hrs, the end of charge "on charge" voltage being 1-45 volts. Overcharging should be avoided, it produces heat and shortens the long term life of the cell.